Wireless networks, such as wireless sensor networks, serve a wide variety of applications, including monitoring, imaging, and tracking, for industrial and military applications. Many existing wireless networks rely on a media access control (MAC) layer using time division multiple access (TDMA) protocols to manage the communication between nodes of the wireless network. The design of the MAC layer and TDMA protocols must take into account the possible complexities of the network involving mobile nodes and energy consumption considerations. Energy efficiency is particularly important for certain sensor or actuator devices with lifetimes determined by the built-in batteries of the devices.
TDMA protocols enable multiple nodes to share a single communication channel by partitioning the communication channel into multiple slots. However, communication in a network with existing TDMA-based MAC layers typically requires one or more central or beacon controllers to coordinate the allocation and timing of the slots. In addition to coordinating the TDMA schedules, central control is necessary to maintain synchronization of the nodes. The scalability of existing centralized wireless networks, however, is inherently limited as a central controller can only manage a finite number of nodes. Furthermore, for networks having mobile nodes, the central controller must also account for nodes joining and leaving the network. For large networks, this accounting can be prohibitively burdensome.
In addition to being centralized, existing networks typically communicate using address-specific messaging. In other words, a transmitted message must include an address for the recipient. The use of addresses requires each node to know, store, and process information regarding other nodes in the network, which can be time and energy consuming. Address-specific messaging also generally requires RTS (request to send), CTS (clear to send), or ACK (acknowledge) messages or functions, which further increases usage of energy and time.
The TDMA protocols used in existing wireless networks typically possess fixed properties, such as the number and allocation of the TDMA communication slots. For networks with high node density, collisions often occur because the fixed TDMA protocols are inadequate for the large number of nodes transmitting and receiving messages and cannot adjust to accommodate the required high data rates. On the other hand, for networks with low node density, the number and allocation of TDMA communication slots are often in excess of the actual usage by the network. Under the latter situation, resources can be wasted and performance may suffer.
The present invention addresses at least the difficult problems of communication in a wireless network and advances the art with a TDMA-based MAC protocol for communication in an ad-hoc distributed wireless network.